Polyolefins such as high density polyethylene (HDPE) homopolymer and linear low density polyethylene (LLDPE) copolymer can be produced using various combinations of catalyst systems and polymerization processes. Ziegler-Natta and chromium-based catalyst systems can, for example, produce ethylene polymers having good extrusion processability and polymer melt strength and bubble stability in blown film applications, typically due to their broad molecular weight distribution (MWD). Further, films produced using Ziegler-Natta catalyst systems have good tear resistance in both the machine direction (MD) and the transverse direction (TD), but generally suffer from poor impact strength. In contrast, metallocene-based catalyst systems can, for example, produce ethylene polymers having excellent impact strength and optical properties, but often lack superior tear resistance, particularly in the machine direction.
In some end-uses, such as blown film applications, it can be beneficial to have the impact resistance and optical properties of a metallocene-catalyzed LLDPE copolymer, but with improved MD tear resistance. Accordingly, it is to these ends that the present invention is generally directed.